h a l f b a k e r y
It's as much a hovercraft as a pancake is a waffle.
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Build a hang glider, slightly larger than standard, with two layers of black solar collective material for the wing. If the volume of heated air contained within the wing is equal to the amount needed to lift you off of the ground by a solar hot air balloon, then vertical take off in a hang glider could
be done from ones own back yard, (I've got this phobia about jumping off of cliffs).
Once a reasonable attitude is achieved the pilot can open valves which release as much or as little of the hot air as is necessary to begin soaring.
By giving the pilot control of lift the only thing forcing you to land is sunset.
Solar hot air balloon.
DrCurry's link to another idea. [2 fries shy of a happy meal, Feb 26 2005]
reminds me of this one...
[po, Feb 26 2005]
||(I've got this phobia about jumping off of cliffs)
||slightly larger than standard... volume needed to lift you off the ground.
||This is a biiiiiiiig hang glider. [+]
||Even with an outsize wing (perhaps
1000 cubic feet of air, which would be a
big thick wing, as [david_s] points out),
and with good solar heating, you'd only
get a few kg of lift - less than the extra
weight of the larger wing, I think. Even
hot-air balloons need burners to get
the air hot enough to give sufficient lift,
and their volume/payload ratio must be
much much higher.
||Not necessarily true [Basepair], see link.
||Well really, [2-fries] - if you wanted
people to follow the link you should
have given it an obvious title! ;-)
||I am impressed, but it's still clear that a
flyable wing wouldn't have sufficient lift,
||I don't think it clear at all.
If the volume of hot air is sufficient for lift, and if the wing is aerodynamically shaped this will work, it will just have a very large wingspan.
||Not necessarily. If you try to make a
very long wing (long enough to have the
same volume as the man-lifting
balloon), you need a lot of framework to
keep it tolerably rigid. Admittedly,
airships have a rigid frame, but (a) they
are not as long and thin as a wing -
they're not long cantilever structures;
and (b) they need helium to get useful
lift (helium has a lower density than
manageably hot air, I think). What I'm
getting it is that I don't think you can
make a lighter-than air hot-air balloon
with an aerodynamically stiff wing-
shape, however you scale it.
***However***, I'm not trying to pick
holes, and I may be wrong. Tell me the
dimensions of the wing you had in mind
and I'll take it all back :-)
||Is there an engineer in the house?
||I think there are a few engineers in the house but I am not one of them so I have no numbers for lift to weight ratios.
It's size would be roughly bigger than a bread box yet smaller than a Cessna.
||A quick calculation. Suppose your
glider is the same size as one of the
wings of a Boeing 747-300 (one wing is
about 90ft long and maybe 18ft front to
back and 3ft top-to-bottom, as a rough
average). If completely hollow, it will
hold about 180 cubic metres of air, give
or take. Suppose that you can solar-
heat this up to the boiling point of
water (100°C), and that the outside
temperature is freezing (to give you the
best lift). In this case, the wing will give
a "hot air" lift of about 62kg. Even a
hang-glider weighs ?30kg?, so a wing
which is five times longer is going to
weigh easily more than 62kg. Hence,
even a wing this size is not going to be
self-lifting in a balloon kind of way.
Sorry, not getting at you - just an
interesting idea and I was curious about
||Well that sucks, I thought for sure that this would be the one idea that finally made me rich.
||[Po] May I please ask you to explain that link? I really don't see any connection.
||:-( sorry. If it's any consolation, the
President of Boeing corporation
probably *is* rich, but is probably
unhappy. Well, maybe.
||So it is basically a solar heated hot air balloon?